Oxytocin scientist studies what makes humans good and evil

The American academic Paul Zak is renowned among his colleagues for two things that he does to people disconcertingly soon after meeting them. The first is hugging: seeing me approach across the library of his club, in midtown Manhattan, New York, he springs to his feet, ignoring my outstretched hand, and enfolds me in his arms. The second is sticking needles in their arms to draw blood.

In the event, I escape our encounter unpunctured, but plenty of people don’t: Zak’s work, which he refers to as ”vampire studies”, has involved extracting blood from a bride and groom on their wedding day; from people who have just had massages, or been dancing; from Quakers, before and after their silent worship; and from tribal warriors in Papua New Guinea as they prepare to perform traditional rituals.

That all these people submit so willingly to his needle may have something to do with the fact that he is charm personified. A square-jawed, 50-year-old Californian with good hair, a sunny disposition and a media-friendly nickname (“Dr Love”), Zak gives every impression of having been constructed in a laboratory charged with creating the ideal deliverer of TED talks. “For further information, to request an interview, or even just a hug from Dr Love,” reads the press release that accompanies his new book, The Moral Molecule, “please contact …”

What drives Zak’s hunger for human blood is his interest in the hormone oxytocin, about which he has become one of the world’s most prominent experts. Long known as a female reproductive hormone – it plays a central role in childbirth and breastfeeding – oxytocin emerges from Zak’s research as something much more all-embracing: the “moral molecule” behind all human virtue, trust, affection and love, “a social glue”, as he puts it, “that keeps society together”. The subtitle of his book, “the new science of what makes us good or evil”, gives a sense of the scale of his ambition, which involves nothing less than explaining whole swaths of philosophical and religious questions by reference to a single chemical in the bloodstream. Being treated decently, it turns out, causes people’s oxytocin levels to go up, which in turn prompts them to behave more decently, while experimental subjects given an artificial oxytocin boost – by means of an inhaler – behave more generously and trustingly. And it’s not solely because of its effects on humans that oxytocin is known as “the cuddle hormone”: for example, male meadow voles, normally roguishly promiscuous in their interactions with female meadow voles, become passionately monogamous when their oxytocin levels are raised in the lab.

The aforementioned wedding – of the New Scientist reporter Linda Geddes and her fiance – took place at a country house in Devon, where Zak set up a temporary research station. He took blood samples, before and after the wedding vows, from the bride and groom, close family members, and various friends in attendance, then flew back his spoils – 156 test tubes, packed in dry ice – to his laboratory at Claremont University, in southern California. There, he discovered the results he had been expecting: the ceremony caused oxytocin to spike in the guests. And it did so in spookily subtle ways: the bride recorded the highest increase, followed by close family members, then less closely involved friends, “in direct proportion to the likely intensity of emotional engagement in the event”. (Only the groom bucked the trend: testosterone interferes with oxytocin, and his testosterone was surging.) Mapping the wedding’s oxytocin levels gave rise, in Zak’s vivid phrase, to a human “solar system” with the bride as the sun, the hormone finely calibrated to the emotional warmth each guest felt. “It was amazing,” Zak recalls. “Just this perfect sense of how oxytocin attunes to the environment.”

The starting point was a persistent mystery in Zak’s original field, economics: time and again, in experiments, people behave more generously than traditional economic models predict that they should. A classic demonstration of this is known as the Trust Game, in which pairs of participants communicate with each other via computer terminals: they never meet, and have no idea who the other person is. Person A is given £10, then invited to send a portion of it, electronically, to person B. Person A has a motive for doing so: according to the rules, which both players know about, any money that A sends to B will triple in value, whereupon B will have the option of sending some of it back as a thank-you. According to conventional notions of rational behaviour, the game should break down before it has begun. Person B, acting selfishly, has no reason to give any money back — and, knowing this, person A shouldn’t send any over in the first place.

Yet, in trials of the game, 90% of A-people send money, while 95% of B-people send some back. Analysis of the oxytocin in their bloodstreams reveals what is going on: by sending money to person B, person A is giving a sign of trust – and being on the receiving end of a sign of trust, it emerges, causes oxytocin to increase, motivating more generous behaviour in return. And it is not just receiving free money that causes people to feel oxytocin’s “warm glow”: in other studies Zak has conducted, random windfalls don’t cause nearly so much of it to be released. What counts is being trusted: trust in one person triggers oxytocin in the other, which triggers more trustworthy behaviour, and so on, in a virtuous circle. “Well, that’s except for the 5% of people who are ‘unconditional non-reciprocators’,” says Zak, referring to the consistent minority of people who seem immune to this cycle. “What we call them in my lab is ‘bastards’.”

These findings have striking implications for how we think about morality. Economists tend to pride themselves on being hardheaded realists: morality might be a nice set of ideas about how people ought to behave, this way of thinking goes, but economics is the analysis of how they really behave, motivated not by stirring ethical values but by the desire for personal gain. Perhaps ironically, religions tend to share a similar view: that moral conduct doesn’t come naturally, but instead needs to be imposed through fear or the promise of reward. Zak himself was raised in a staunch Catholic household: his mother, he likes to say, took him out of Catholic school because it wasn’t strict enough, and “based her child-rearing on the assumption that unselfish, moral behaviour was impossible without the ever-present threat of punishment, the more terrifying the better”. Yet the fact that natural selection has given us oxytocin – a mechanism that allows us to be instinctively trusting and kind – suggests that what most of us think of as “moral” is, in fact, part of how we have evolved to be.

“Human beings are almost the only animals who regularly want to be around strange members of our species,” Zak says. “We kind of dig it! It’s fun! But to be able to do that, we have to have something in our heads that says: ‘Oliver is safe, Bob is not safe.’ And that’s oxytocin – this very old, evolutionarily ancient molecule” that helps us respond to being trusted with just the right degree of reciprocal trust in response. Zak’s earlier work had established that trust is a crucial precondition for economic prosperity (to conduct transactions, you have to be able to trust others) but also a result of it (once you’re no longer fighting for basic subsistence, you can afford to trust more). Now, he had located the biological mechanism through which this all worked. The Golden Rule – treat others as you’d like to be treated – is, Zak writes, “a lesson that the body already knows”.

From that follows … well, everything. “To me, this is the basis for civilisation: a bunch of strangers living together,” he says. “And once you have civilisation, you can have specialisation of labour; you can have surplus; you can have university professors, and priests, because now you can afford that, and then you get the advancement of knowledge.”

This talk of mixing science and morality prompts suspicion in some quarters: just because something is “natural” doesn’t mean it is “right”, in an ethical sense, and efforts to derive codes of moral conduct from science rarely end well. (Sam Harris’s recent book, The Moral Landscape: how science can determine human values, is one such car crash: all it really shows is how science could be used to help construct Harris’s version of a perfect society, which isn’t the same point at all.) Moreover, it is unclear what Zak means when he says oxytocin, or the lack of it, “makes” us good or evil. This is the same problem as with news reports about scientists discovering the part of the brain “responsible for” risk-taking, or greed, or a belief in God: just because you have found the biological underpinnings of some phenomenon, it does not necessarily follow that you have found “the real cause” of it. Still, none of that undermines the most potent aspect of Zak’s work, which is the pragmatic one. If oxytocin is the mechanism through which moral action takes place, that holds out the possibility – a cause of either optimism or alarm, depending on how you look at it – that by manipulating oxytocin, we might boost the levels of trust, generosity, and ultimately happiness in ourselves and the world at large.

It took Zak two years of wrangling with the US Food and Drug Administration and university ethics panels to gain approval to use oxytocin inhalers on experimental subjects. (In the meantime, he got around the restriction by experimenting on himself, under the watchful eye of his wife, a practising neurologist.) But while the red tape was convoluted, the eventual conclusions were not: in exercises such as the Trust Game, oxytocin-loaded participants displayed much greater levels of trust and generosity than those who used inhalers filled with a placebo.

All of which would seem to raise some troubling questions: what is to stop car dealers, say, pumping oxytocin into showrooms, or politicians using it when canvassing? (A company called Vero Labs already markets an oxytocin spray it calls “Liquid Trust”, aimed both at salespeople and single men on the prowl.) But Zak waves the matter away: it is incredibly hard to get enough oxytocin into the bloodstream, which is why he has to get his subjects to force such large amounts of vapour up their noses; using it covertly would never work. Sure, oxytocin can be stimulated in subtle ways to serve other people’s agendas, “but they’re already doing that. Why do you think they have cute puppies in toilet paper commercials? To make you feel good,” by provoking the release of oxytocin.

Meanwhile, Zak says, we should all be doing more to boost oxytocin in benign ways. He recommends a minimum of eight hugs a day (pets count, too); massage and even soppy movies seem to work: he has done the blood tests. Interactions on Twitter and Facebook seem to lead to oxytocin spikes, offering a powerful retort to the argument that social media is killing real human interaction: in hormonal terms, it appears, the body processes it as an entirely real kind of interaction.

The political implications are a little unclear: Zak describes himself as a political agnostic, but speaks approvingly of David Cameron’s “Big Society” ideas, since interactions in small groups tend to work better, in oxytocin terms, than larger government structures. Then again, the untrammelled self-interest of free-market fundamentalists is surely a recipe for oxytocin depletion: prosperity, Zak’s work shows, emerges in harmony with trust and kindness, not selfishness. Ultimately, one imagines, the oxytocin-savvy citizens of Zak’s version of utopia would live on a local scale, supported by a social safety net, but with a focus on charity work and community groups. They would play with their pets, and watch romantic comedies. Perhaps above all, they would be very touchy-feely, and hug each other all the time – which makes you wonder whether, in Britain, the prescriptions of Dr Love might not be a bit of a lost cause.

• The Moral Molecule is published by Bantam, price £16.99. To order a copy for £13.59 with free UK p&p, go to guardian.co.uk/bookshop or call 0330 333 6846.